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United States Patent |
6,037,086
|
Gorog
,   et al.
|
March 14, 2000
|
Method of manufacturing a matrix for a cathode-ray tube
Abstract
A light-absorbing matrix 23, having openings therein, is formed on an
interior surface of a faceplate panel 12 of a cathode-ray tube 10 by
providing a photoreceptor thereon, electrostatically charging the
photoreceptor 72 to a substantially uniform level of charge, and exposing
the photoreceptor to light through openings 33 in a color selection
electrode 24 to selectively discharge the more intensely illuminated areas
of the photoreceptor, without substantially discharging the less intensely
illuminated areas. The photoreceptor 72 comprises a plurality of layers
including a photoresist layer 56, a conductive layer 62, and a
photoconductive layer 66. The openings 33 in the color selection electrode
24 have a dimension substantially greater than the dimension of the
openings in the resultant matrix 23.
The photoreceptor 72 is contacted with a liquid toner having charged
pigment particles which form toner lines 84 on the less intensely
illuminated areas of the photoreceptor. The photoreceptor 72 is exposed to
UV radiation to selectively change the solubility of the photoresist
portion 56 thereof into areas of greater and lesser solubility. The
photoreceptor 72 is serially developed to expose portions of the interior
surface of the panel 12, while leaving the areas of lesser solubility
intact. Next, the interior surface of the panel and the areas of lesser
solubility are coated with a matrix suspension which is dried to form the
matrix 23. The areas of lesser solubility and the overlying
light-absorbing matrix material thereon are removed, thereby forming in
the matrix 23 a plurality of openings having a width less than the width
of the openings 33 in the color selection electrode 24.
Inventors:
|
Gorog; Istvan (Lancaster, PA);
LaPeruta, Jr.; Richard (Lititz, PA);
Pearlman; Samuel (Lancaster, PA);
Desai; Nitin Vithalbher (Princeton Junction, NJ);
Stewart; Wilber Clarence (Hightstown, NJ);
Cohee; Gregory James (Newtown, PA);
Nosker; Richard William (Princeton, NJ);
Datta, deceased; Pabitra (late of Cranbury, NJ);
Herford; Danielle Helene (Etters, PA)
|
Assignee:
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Thomson Consumer Electronics, Inc., (Indianapolis, IN)
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Appl. No.:
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097390 |
Filed:
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June 16, 1998 |
Current U.S. Class: |
430/25; 430/119 |
Intern'l Class: |
G03G 013/10 |
Field of Search: |
430/25,28,24,29,100,119
|
References Cited
U.S. Patent Documents
3558310 | Jan., 1971 | Mayaud | 96/36.
|
4921767 | May., 1990 | Datta et al. | 430/23.
|
5455133 | Oct., 1995 | Gorog et al. | 430/23.
|
5519217 | May., 1996 | Wilbur et al. | 250/326.
|
5646478 | Jul., 1997 | Nosker et al. | 313/402.
|
5744270 | Apr., 1998 | Pearlman et al. | 430/25.
|
5840450 | Nov., 1998 | Cho | 430/25.
|
Other References
A.M. Morrell et al., Color Television Picture Tubes, pp. 80-85 (1974).
|
Primary Examiner: Rodee; Christopher D.
Attorney, Agent or Firm: Tripoli; Joseph S., Irlbeck; Dennis H.
Claims
What is claimed is:
1. A method of manufacturing a light-absorbing matrix having a plurality of
openings formed therein on an interior surface of a faceplate panel of a
cathode-ray tube, comprising the steps of:
a) forming a photoreceptor, having a plurality of layers including a
photoresist layer, a conductive layer, and a photoconductive layer, on
said interior surface of said faceplate panel;
b) electrostatically charging said photoreceptor to a substantially uniform
level of charge;
c) inserting a color selection electrode into said panel, said color
selection electrode having a major axis and a minor axis with a plurality
of openings each having a first transverse dimension along said major
axis;
d) exposing said photoreceptor to light, through said plurality of openings
in said color selection electrode, to selectively discharge the more
intensely illuminated areas of said photoreceptor, without substantially
discharging the less intensely illuminated areas thereof;
e) removing said color selection electrode from said panel;
f) contacting said photoreceptor with a suitable liquid toner to form a
plurality of toner locations, said toner comprising pigment particles
having a charge opposite in polarity to the charge on the less intensely
illuminated areas of said photoreceptor;
g) reinserting said colorselection electrode into said panel;
h) re-exposing said photoreceptor to light to selectively change the
solubility of said photoresist portion of said photoreceptor, thereby
creating in said photoresist portions areas of greater solubility
underlying said toner locations and areas of lesser solubility
therebetween;
i) serially developing said photoreceptor to expose portions of said
interior surface of said panel, while leaving said areas of lesser
solubility;
j) coating said exposed portions of said interior surface of said panel and
said areas of lesser solubility with a matrix suspension;
k) drying said matrix suspension to form a light-absorbing matrix; and
l) contacting said light-absorbing matrix with a solvent to remove said
areas of lesser solubility and the overlying light-absorbing matrix
thereon, without removing said light-absorbing matrix from the exposed
portions of said interior surface of said panel, thereby forming, in said
light-absorbing matrix, said plurality of openings each having a second
transverse dimension along said major axis, whereby said first transverse
dimension of said openings in said color selection electrode is
substantially greater than said second transverse dimension of said
openings in said matrix.
2. The method as described in claim 1, further including, prior to step a),
the substep of coating said interior surface of said faceplate panel with
a PVA solution to form a precoat layer.
3. The method as described in claim 2, where step a) includes the substeps
of:
I) overcoating said precoat layer with a photoresist solution to form said
photoresist layer;
II) overcoating said photoresist layer with an organic conductive solution
to form an organic conductive (OC) layer;
III) overcoating said OC layer with an organic photoconductive solution to
form an organic photoconductive (OPC) layer; and
IV) applying a PVPy solution to said OPC layer to form a protective coating
thereon.
4. The method as described in claim 3, wherein step i), which recites
serially developing said photoreceptor to expose portions of said interior
surface of said panel while leaving said areas of lesser solubility,
includes:
depositing a first solvent into said panel to remove said toner locations
and said protective coating;
depositing a second solvent into said panel to remove said OPC layer, and
depositing a third solvent into said panel to remove said OC layer and said
areas of greater solubility of said photoresist layer, thereby exposing
portions of said interior surface of said panel, while leaving intact said
areas of said photoresist layer of lesser solubility.
5. The method as described in claim 4, wherein said first solvent is
selected from the group consisting of IPA, an aqueous solution of sulfamic
acid (15%), and periodic acid (10%).
6. The method as described in claim 4, wherein said second solvent is
selected from the group consisting of a mixture of toluene and MIBK, and
D-limonene.
7. The method as described in claim 4, wherein said third solvent is water.
8. The method as described in claim 2, where step a) includes the substeps
of:
I) overcoating said precoat layer with a suitable solution to form a single
photoresist and OC layer;
II) overcoating said single photoresist and OC layer with an organic
photoconductive solution to form an organic photoconductive (OPC) layer;
and
III) applying a PVPy solution to said OPC layer to form a protective
coating thereon.
9. A method of manufacturing a light-absorbing matrix having a plurality of
rectangular matrix openings formed therein on an interior surface of a
faceplate panel of a cathode-ray tube, comprising the steps of:
coating said interior surface of said faceplate panel with a PVA solution
to form a precoat layer;
overcoating said precoat layer with a photoresist solution to form a
photoresist layer;
overcoating said photoresist layer with an organic conductive solution to
form an organic conductive (OC) layer;
overcoating said OC layer with an organic photoconductive solution to form
an organic photoconductive (OPC) layer;
applying a PVPy solution to form a protective overcoating on said OPC
layer;
electrostatically charging said OPC layer to a substantially uniform level
of charge;
inserting, into said panel, a tension focus mask having a major axis and a
minor axis with a plurality of rectangular slots which are parallel to
said minor axis, said slots having a first width which is parallel to said
major axis;
exposing to light said OPC layer, through said plurality of rectangular
slots in said tension focus mask, from at least five light locations, to
selectively discharge the more intensely illuminated areas of said OPC
layer, without substantially discharging the less intensely illuminated
areas of said OPC layer;
removing said tension focus mask from said panel;
contacting said OPC layer with a suitable liquid toner, having charged
pigment particles therein, to form a plurality of toner lines on the less
intensely illuminated areas of said OPC layer, said pigment particles
having a charge opposite in polarity to the charge on the less intensely
illuminated areas of said OPC layer;
reinserting said tension focus mask into said panel;
flood exposing said photoresist layer underlying said protective layer,
said OPC layer and said OC layer, to UV radiation to selectively change
the solubility thereof, thereby creating in said photoresist layer areas
of greater solubility underlying said toner lines and areas of lesser
solubility therebetween;
depositing a first solvent into said panel to remove said toner lines and
said protective coating;
depositing a second solvent into said panel to remove said OPC layer;
depositing a third solvent into said panel to remove said OC layer and said
areas of said photoresist layer of greater solubility, thereby exposing
portions of the underlying interior surface of said panel, while leaving
intact said areas of said photoresist layer of lesser solubility;
coating said exposed portions of said interior surface of said panel and
said areas of said photoresist layer of lesser solubility with a matrix
suspension;
drying said matrix suspension to form a layer of said light-absorbing
matrix; and
depositing a fourth solvent into said panel to remove said areas of said
photoresist layer of lesser solubility and the overlying matrix thereon,
thereby forming in said light-absorbing matrix a plurality of rectangular
openings having a second width which is parallel to said major axis,
whereby the first width of said rectangular slots in said tension focus
mask is substantially greater than the corresponding second width of said
rectangular openings in said matrix.
10. The method as described in claim 9, wherein said first solvent is
selected from the group consisting of IPA, an aqueous solution of sulfamic
acid (15%), and periodic acid (10%).
11. The method as described in claim 9, wherein said second solvent is
selected from the group consisting of a mixture of toluene and MIBK, and
D-limonene.
12. The method as described in claim 9, wherein said third solvent is
water.
13. The method as described in claim 9, wherein said fourth solvent is
aqueous periodic acid.
14. A method of manufacturing a light-absorbing matrix having a plurality
of rectangular matrix openings formed therein on an interior surface of a
faceplate panel of a cathode-ray tube, comprising the steps of:
coating said interior surface of said faceplate panel with a PVA solution
to form a precoat layer;
combining a photoresist and organic conductive solution to form a
photoresist-conductive layer;
overcoating said photoresist-conductive layer with an organic
photoconductive solution to form an organic photoconductive (OPC) layer;
applying a PVPy solution to form a protective overcoating on said OPC
layer;
electrostatically charging said OPC layer to a substantially uniform level
of charge;
inserting, into said panel, a tension focus mask having a major axis and a
minor axis with a plurality of rectangular slots which are parallel to
said minor axis, said slots having a first width which is parallel to said
major axis;
exposing to light said OPC layer, through said plurality of rectangular
slots in said tension focus mask, from at least five light locations, to
selectively discharge the more intensely illuminated areas of said OPC
layer, without substantially discharging the less intensely illuminated
areas of said OPC layer;
removing said tension focus mask from said panel;
contacting said OPC layer with a suitable liquid toner, having charged
pigment particles therein, to form a plurality of toner lines on the less
intensely illuminated areas of said OPC layer, said pigment particles
having a charge opposite in polarity to the charge on the less intensely
illuminated areas of said OPC layer;
reinserting said tension focus mask into said panel;
flood exposing said photoresist-conductive layer underlying said protective
layer, and said OPC layer, to UV radiation to selectively change the
solubility thereof, thereby creating in said photoresist-conductive layer
areas of greater solubility underlying said toner lines and areas of
lesser solubility therebetween;
depositing a first solvent into said panel to remove said toner lines and
said protective coating;
depositing a second solvent into said panel to remove said OPC layer;
depositing a third solvent into said panel to remove areas of said
photoresist-conductive layer of greater solubility, thereby exposing
portions of the underlying interior surface of said panel, while leaving
intact said areas of said photoresist-conductive layer of lesser
solubility;
coating said exposed portions of said interior surface of said panel and
said areas of said photoresist-conductive layer of lesser solubility with
a matrix suspension;
drying said matrix suspension to form a layer of said light-absorbing
matrix; and
depositing a fourth solvent into said panel to remove said areas of said
photoresist-conductive layer of lesser solubility and the overlying matrix
thereon, thereby forming in said light-absorbing matrix a plurality of
rectangular openings having a second width which is parallel to said major
axis, whereby the first width of said rectangular slots in said tension
focus mask is substantially greater than the corresponding second width of
said rectangular openings in said matrix.
Description
This invention relates to a method of manufacturing a light-absorbing
matrix for a cathode-ray tube (CRT) and, more particularly to a method of
making a matrix using a color selection electrode having openings
substantially greater in width than the width of the resultant matrix
openings.
BACKGROUND OF THE INVENTION
FIG. 1 shows a shadow mask 2 and a viewing faceplate 18 of a conventional
CRT screen surface having a screen assembly 22 thereon. The shadow mask 2
includes a plurality of slits, or rectangular openings, 4 only one of
which is shown. The screen assembly 22 includes a light-absorbing matrix
23 with rectangular openings in which blue-, green-, and red-emitting
phosphor lines, P.sub.b, P.sub.g and P.sub.r, respectively, are disposed.
Three color-emitting phosphors and the matrix lines, or guardbands,
therebetween comprise a triad having a width, or screen pitch, T, of about
0.84 mm (33 mils). The guardbands are designated hereinafter as RB, for
the guardbands between the red- and blue-emitting phosphor lines; RG, for
the guardbands between the red- and green-emitting phosphor lines; and BG,
for the guardbands between the blue- and green-emitting phosphor lines.
For the conventional shadow mask 2, the mask openings 4 have a width, a,
not greater than one third the width, T, of the triad. In a CRT having a
diagonal dimension of 51 cm (20 inches), the width, a, of the shadow mask
openings 4 are on the order of about 0.23 mm (9 mils) and the resultant
openings formed in the matrix have a width, c, of about 0.18 mm (7 mils).
The guardbands of the matrix 23, between the adjacent phosphor lines, have
a width, d, of about 0.1 mm (4 mils). The matrix 23, preferably, is formed
on the viewing faceplate 18 by the process described in U.S. Pat. No.
3,558,310, issued to Mayaud on Jan. 26, 1971. Briefly, a film of a
suitable photoresist, whose solubility is altered by light, is provided on
the interior surface of the viewing faceplate 18. The photoresist film is
exposed, through the openings 4 in the shadow mask 2, to ultraviolet light
from a conventional three-in-one lighthouse, shown schematically in FIG.
2. With the shadow mask 2 in place, the photoresist film is exposed
sequentially and equally (6 exposures units (wgt) each, for example) by
each of the light sources. The shadow mask openings 4 have a periodic
pitch, D.sub.m, and the design value of the mask-to-screen spacing is
Q=Q.sub.0. It is desired that the light paths from the three sources, R, G
and B, mimic the electron beam paths from the three electron guns of the
CRT. Therefore, the light sources R, G and B are spaced a distance, L,
from the screen, at the effective center of deflection of the gun-yoke
system, and are laterally spaced by the same distance, s, as the electron
beam centers in the deflection plane. The "G" source lies on the symmetry
axis of the screen and mask.
After the matrix exposure process is completed, the regions of the
photoresist film with greater solubility are removed by flushing the
exposed film with water, thereby uncovering bare areas of the faceplate.
Next, the interior surface of the faceplate panel is overcoated with a
black matrix slurry, of the type known in the art, which, when dried, is
adherent to the uncovered areas of the faceplate. Finally, the matrix
material overlying the retained film regions, as well as the retained film
regions, are removed, leaving the matrix guardbands on the previously
uncovered areas of the faceplate panel. The positions on the screen
surface denoted by b, g and r in FIG. 2, are the centers of the projected
slit images. The matrix guardbands are in the area of least light
exposure, midway between the slit images. From the exposure geometry, the
design value of the triad pitch, T, at the screen, based on the projected
slit images from a single light source, is given by:
T=(L/(L-Q.sub.0)).times.D.sub.m. (1)
In order to obtain the required value of T/3 for the distance from g to b,
and for the distance from r to g at the screen, the condition,
s=LD.sub.m /3Q.sub.0 (2)
must be met, where "s" is the lateral spacing between the light sources in
the lighthouse, as shown in FIG. 2.
Again with reference to FIG. 1, the difference between the width, a, of the
shadow mask openings and the width, c, of the matrix openings is referred
to as "print down." Thus, in the conventional shadow mask-type CRT, having
mask openings with a width of 0.23 mm and the matrix openings with a width
of 0.18 mm, the typical "print down" is about 0.05 mm (2 mils). A drawback
of the shadow mask-type CRT is that, at the center of the screen, the
shadow mask intercepts all but about 18-22% of the electron beam current;
that is, the shadow mask is said to have a transmission of only about
18-22%. Thus, the area of the openings 4 in the shadow mask 2 is about
18-22% of the area of the mask. Because there are no focusing fields
associated with the shadow mask 2, a corresponding portion of the screen
assembly 22 is excited by the electron beams.
In order to increase the transmission of the color selection electrode
without increasing the size of the excited portions of the screen, a
post-deflection focusing color selection structure is required. The
focusing characteristics of such a structure permit larger aperture
openings to be utilized to obtain greater electron beam transmission than
can be obtained with the conventional shadow mask. One such structure, a
uniaxial tension focus mask, is described in U.S. Pat. No. 5,646,478
issued to R. W. Nosker et al. on Jul. 8, 1997. A drawback of using a post
deflection color selection electrode, such as a tension focus mask, is
that conventional methods for forming the matrix cannot be utilized,
because the prior methods provide only about a 0.05 mm (2 mil) "print
down." For the tension focus mask of U.S. Pat. No. 5,646,478, the triad
period or pitch, T, of the screen assembly is the same as for a CRT with a
conventional shadow mask, so the matrix openings are about 0.18 mm wide.
However, as described hereinafter, for a tension focus mask-type CRT, a
"print down" of about 0.37 mm (14.5 mils) is required. Such a high degree
of "print down" cannot be achieved with the conventional matrix process
described above. Additionally, for a tension focus mask-type CRT having,
for example, 50% mask transmission, any matrix opening patterns formed
using a conventional three-in-one lighthouse process, such as that taught
by Mayaud, referenced above, will result in misregister of the electron
beams which impinge upon the blue- and red-emitting phosphors and also
nonparity of the intratrio openings with "Q"-space errors. "Q"-space
errors of the order of +/-5%, that is variations in the focus
mask-to-screen spacing caused by deviations of the faceplate thickness or
curvature from the bogie dimensions, are typical. Accordingly, a new
method of making a matrix with the capability for very large "print down"
is required.
SUMMARY OF THE INVENTION
The present invention relates to a method of manufacturing a
light-absorbing matrix, having a plurality of openings formed therein, on
an interior surface of a faceplate panel of a cathode-ray tube. A
photoreceptor, having a plurality of layers including a photoresist layer,
a conductive layer, and a photoconductive layer, is formed on the interior
surface of the panel and electrostatically charged to a substantially
uniform level of charge. Then, a color selection electrode having a
plurality of openings, substantially greater in a dimension than the
corresponding openings in the light-absorbing matrix, is inserted into the
panel. The photoreceptor is exposed to light through the openings in the
color selection electrode to selectively discharge the more intensely
illuminated areas of the photoreceptor, without substantially discharging
the less intensely illuminated areas and without substantially irradiating
the underlying photoresist. The color selection electrode is removed from
the panel after the exposure step, and the photoreceptor is contacted with
a suitable liquid toner to form toner lines. The liquid toner comprises
pigment particles having a charge opposite in polarity to the charge on
the less intensely illuminated areas of the photoreceptor. The color
selection electrode is re-inserted into the panel and the photoreceptor is
exposed to UV radiation to selectively change the solubility of the
photoresist layer thereof, thus creating areas of greater solubility
underlying the toner lines and areas of lesser solubility therebetween.
The photoreceptor is serially developed to remove the areas with lesser
solubility and expose portions of the interior surface of the panel, while
leaving intact the areas of lesser solubility. Next, the exposed portions
of the interior surface of the panel and the areas of lesser solubility
are coated with a matrix suspension and dried to form a matrix. The matrix
is developed by contacting it with a solvent to remove the areas of lesser
solubility and the overlying light-absorbing matrix thereon, without
removing the light-absorbing matrix from the exposed portions of the
interior surface of the panel.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is an enlarged sectional view of a portion of a conventional shadow
mask and screen of a CRT demonstrating "print-down";
FIG. 2 schematically shows a conventional three-in-one lighthouse exposure
procedure used in conjunction with a shadow mask;
FIG. 3 is a plan view, partly in axial section, of a color CRT made
according to the present invention;
FIG. 4 is an enlarged sectional view of a portion of the tension focus mask
and screen of the CRT of FIG. 3;
FIG. 5 is a plan view of a tension focus mask and frame used in the CRT of
FIG. 3;
FIG. 6A is a partial view of a flow chart of the manufacturing process of
the present invention;
FIG. 6B is a partial view of a flow chart of the manufacturing process of
the present invention, which, with FIG. 6A, is intended to form one
complete view of the manufacturing process;
FIG. 7 is an enlarged sectional view of a portion of a viewing faceplate
having a plurality of layers formed thereon during successive steps in the
matrix manufacturing process;
FIG. 8 schematically shows the exposure procedure described as the entry in
column 4 of the TABLE;
FIG. 9 schematically shows the exposure procedure described as the entry in
column 6 of the TABLE; and
FIG. 10 schematically shows the exposure procedure described as the entry
in column 8 of the TABLE.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 3 shows a cathode-ray tube 10 having a glass envelope 11 comprising a
rectangular faceplate panel 12 and a tubular neck 14 connected by a
rectangular funnel 15. The funnel has an internal conductive coating (not
shown) that extends from an anode button 16 to the neck 14. The panel 12
comprises a cylindrical viewing faceplate 18 and a peripheral flange or
sidewall 20 that is sealed to the funnel 15 by a glass frit 17. A
three-color phosphor screen 22 is carried by the inner surface of the
faceplate 18. The screen 22 is a line screen with the blue-, green-, and
red-emitting phosphors arranged in triads, each triad including a phosphor
line of each of the three colors, P.sub.b, P.sub.g and P.sub.r, separated
by opaque lines of a light-absorbing matrix 23, shown in FIG. 4. A
cylindrical multi-apertured color selection electrode, such as a tension
focus mask, 24 is removably mounted within the panel 12, in predetermined
spaced relation to the screen 22. An electron gun 26, shown schematically
by the dashed lines in FIG. 3, is centrally mounted within the neck 14 to
generate and direct three inline electron beams (also not shown) along
convergent paths through the tension focus mask 24 to the screen 22. The
electron gun is conventional and may be any suitable gun known in the art.
The CRT 10 is designed to be used with an external magnetic deflection
yoke, such as the yoke 30, shown in the neighborhood of the funnel-to-neck
junction. When activated, the yoke 30 subjects the three beams to magnetic
fields that cause the beams to scan a horizontal and vertical rectangular
raster over the screen 22. As is known in the art, an aluminum layer (not
shown) overlies the screen 22 and provides an electrical contact thereto,
as well as a reflective surface to direct light, emitted by the phosphors,
outwardly through the viewing faceplate 18. As shown in FIG. 5, the
tension focus mask 24 is formed, preferably, from a thin rectangular sheet
of about 0.05 mm (2 mil) thick low carbon steel, that includes two long
sides and two short sides. The two long sides of the tension focus mask
parallel the central major axis, X, of the mask and the two short sides
parallel the central minor axis, Y, of the mask. With reference to FIGS. 4
and 5, the tension focus mask 24 includes an apertured portion that
contains a plurality of first elongated strands 32 separated by slots 33
that parallel the minor axis, Y, of the mask. In one configuration, the
mask pitch, D.sub.m, defined as the transverse dimension of a first strand
32 and an adjacent slot 33, is 0.85 mm (33.5 mils). As shown in FIG. 4,
each of the first strands 32 has a transverse dimension, or width, w, of
about 0.39 mm (15.5 mils) and each of the slots 33 has a width, a', of
about 0.46 mm (18 mils). The slots 33 extends from near one long side of
the tension focus mask to near the other long side thereof. A plurality of
second strands 34, each having a diameter of about 0.025 mm (1 mil), are
disposed substantially parallel to the first strands 32 and spaced
therefrom by insulators 36. As shown in FIG. 5, the frame 38 comprises
four major members: two torsion members 40 and 41; and two side members 42
and 43. The two torsion members, 40 and 41, parallel the major axis, X,
and each other. The long sides of the tension focus mask 24 are welded
between the two torsion members 40 and 41 which provide the necessary
tension to the mask 24. Again with reference to FIG. 4, the screen 22,
formed on the viewing faceplate 18, includes the light-absorbing matrix 23
with rectangular openings in which the color emitting phosphor lines are
disposed. The corresponding matrix openings have a width, c, of about 0.25
mm (6.1 mils). The width, d, of each matrix line is about 0.15 mm (5.8
mils) and each phosphor triad has a width or screen pitch, T, of about
0.91 mm (35.8 mils). For this embodiment, the tension focus mask 24 is
spaced at a distance, Q, (hereinafter Q-spacing) of about 15.24 mm (600
mils) from the center of the interior surface of the faceplate panel 12.
During operation of the CRT 10, the voltage difference between the first
strands 32 and the second strands 34, at an anode voltage of 30 kV, is
about 800 volts.
The pitch, D.sub.m, of the tension focus mask 24 can be varied. For
example, in a second configuration, with a mask pitch of 0.68 mm (25.6
mils) and a first strand width of 0.3 mm (11.8 mils), the corresponding
screen pitch, T, is 0.68 mm (26.78 mils). Each matrix opening has a width,
c, of about 0.11 mm (4.5 mils) and a matrix line width, d, of about 0.11
mm (4.5 mils). For this configuration of the tension focus mask 24, with a
center Q-spacing of 11.56 mm (455 mils), the voltage difference between
the first strands 32 and the second strands 34, at an anode voltage of 30
kV, is about 750 volts.
In a third configuration, with a mask pitch, D.sub.m, of 0.41 mm (16.1
mils) and a first strand width of 0.2 mm (7.8 mils), the corresponding
screen pitch, T, is 0.42 mm (16.5 mils). Each matrix opening has a width,
c, of about 0.051 mm (2 mils) and a matrix line width, d, of about 0.089
mm (3.5 mils). For this configuration of the tension focus mask 24, with a
center Q-spacing of 7.4 mm (291.5 mils), the voltage difference between
the first strands 32 and the second strands 34, at an anode voltage of 30
kV, is about 650 volts.
The method of manufacturing the matrix 23 will be described in an
embodiment using the tension focus mask 24 with a mask pitch, D.sub.m, of
0.68 mm as a photographic master. Initially, the panel 12 is cleaned, as
indicated in step 50 of FIG. 6A, by washing it with a caustic solution,
rinsing it in water, etching it with buffered hydrofluoric acid and
rinsing it again with water, as is known in the art. As indicated in step
52, the interior surface of the viewing faceplate 18 of the panel 12 is
then coated with a polyvinyl alcohol (PVA) solution and dried to form a
precoat layer 54, shown in FIG. 7. Because the chemical composition of the
glass faceplate panel 12 may vary somewhat from one glass manufacturer to
another, the precoat layer 54 provides a uniform surface condition for the
deposition for subsequent materials. The thickness of the precoat layer 54
is on the order of a monolayer. A negative photoresist solution is
overcoated onto the precoat layer 54 and dried to form a photoresist layer
56, as indicated in step 58. The photoresist solution comprises 1.08 wt. %
of PVA; 1.08 wt. % PVP; 0.6 wt. % of a sensitizer, such as Diazo Resin #8,
available from Fairmount Chemical Co., Inc., Newark, N.J., 0.02 wt. % of a
surfactant, such as Triton X100, available from Union Carbide, Danbury,
Conn.; and the balance, deionized (DI) water. The photoresist layer 56 has
a thickness of about 1.+-.0.2 .mu.m. Then, an organic conductive solution
is overcoated onto the photoresist layer 56 and dried to form an organic
conductive (OC) layer 62, as indicated in step 60. The thickness of the OC
layer 62 is about 1.+-.0.2 .mu.m. The OC solution comprises about 0.62 wt.
% PVP; 5.84 wt. % MS-905, available from BASF, Parsippany, N.J.; and the
balance, methanol. Next, as indicated in step 64, an organic
photoconductive solution is provided to overcoat the OC layer 62 and dried
to form an organic photoconductive layer (OPC) 66. The OPC layer 66 has a
thickness of about 5.+-.1 .mu.m. The OPC solution comprises about 0.005
wt. % of the surfactant UL-7602, available from Union Carbide, Danbury,
Conn.; about 0.23 wt. % of 2,4,7-trinitro-9-fluorenone (TNF); about 0.35
wt. % of 2-ethylanthraquinone (EAQ); about 2.32 wt. % of
tetraphenylethylene (TPE); about 9.28 wt. % polystyrene; about 24.49 wt. %
xylene; and the balance, toluene. Then, as indicated in step 68, a
poly-2-vinylpyridine (PVPy) solution is applied to overcoat the OPC layer
66 and dried to form a protective layer 70, having a thickness of about
0.7.+-.0.2 .mu.m. The photoresist layer 56, the OC layer 62 and the OPC
layer 66 are referred to hereinafter, collectively, as the photoreceptor
72.
The faceplate panel is then placed on a charging apparatus of the type
described in U.S. Pat. No. 5,519,217, issued to Wilbur et al., on May 21,
1996, and the OPC layer 66 of the photoreceptor 72 is electrostatically
charged to a positive voltage of 425.+-.25V to provide a substantially
uniform level of charge, as indicated in step 74. As indicated in step 76,
the tension focus mask 24 is inserted into the faceplate panel 12 and
mounted within a lighthouse, containing a plurality of light sources.
Unlike a conventional CRT in which the shadow mask 2 has openings 4, each
with a width less than D.sub.m /3, CRT's embodying the tension focus mask
24 may have an opening a' with a width between D.sub.m /3 and 2D.sub.m /3.
If one were to use the three light sources, R, G and B, shown in FIG. 2,
to project an image of the mask openings 33 of FIG. 4, significant spatial
overlap at the screen would occur. The result would be that the area of
least exposure would be centered on the projected image of the opening 33,
where it is intended that one of the phosphor stripes would eventually be
centered. To avoid this problem all of the light source positions of FIG.
2 are laterally shifted, either left or right, by a distance, s/2, so that
the light source, G, no longer lies on the symmetry axis of the screen and
mask. When the light sources are shifted to the right, the mask-screen
axis lies halfway between the shifted R and G light sources. Similarly, if
the light sources are shifted to the left, the screen symmetry axis lies
midway between the shifted G and B light sources. The light source
geometries for the exposure procedures for a conventional CRT with a
shadow mask and a CRT using a tension focus mask 24, are summarized as
entries 1-3 of the TABLE. The TABLE indicates the light source locations
and exposure weights (in parenthesis).
______________________________________
1 2 3 4 5 6 7 8
______________________________________
-5s/2 G'(2) G'(1)
-2s R'(6) R'(2)
-3s/2 B(6) R'(2) R'(4) R'(3)
-s B(6) B(4)
-s/2 B(6) G(6) B(4) B(6) B(5)
0 G(6) G(6) G(6)
+s/2 G(6) R(6) G(6) G(4) G(5)
+s R(6) R(4)
+3s/2 R(6) R(4) R(2) R(3)
+2s B'(6) B'(2)
+5s/2 B'(2) B'(1)
______________________________________
In the TABLE, column 1 indicates the light locations and exposure weights
for the conventional CRT and shadow mask of FIG. 2. Column 2 represents a
CRT using the tension focus mask 24 with the light locations left shifted,
and column 3 represents the same tension focus mask 24 with the light
locations right shifted.
The values of s used to set the locations of the light sources in a
lighthouse are linked to the design values L, D.sub.m, and Q.sub.0. When a
defective or unmatched shadow mask or tension focus mask exhibits location
deformations from the specified surface shape z.sub.m (x, y), the error
produces a local mask-screen spacing of the form Q=Q.sub.0 +.epsilon.,
while L remains fixed. The trio pitch T.sub.1 at the screen becomes:
T.sub.1 =LD.sub.m /[L-(Q.sub.0 +.epsilon.)], (3)
and the spacing x.sub.1 between the image centers g and b and between the
image centers r and g, expressed as a fraction of the .epsilon.-dependent
trio spacing, is given by the relation:
x.sub.1 /T.sub.1 =(Q.sub.0 +.epsilon.)/3Q.sub.0. (4)
The lateral shift of the light sources required for printing screens for a
CRT having a tension focus mask 24 affects only the reference position of
the matrix stripes with respect to the mask openings 33. It has no
influence on the stripe-to-stripe spacing, i.e., such shifting of the
source does not change the screen structure elements or their relationship
to each other, but rather laterally shifts them collectively with respect
to the mask. Therefore, the spacing formulas of equations (3) and (4)
apply to both conventional CRT and to CRT having the tension focus mask
24. For both types of tubes, errors of .+-.5% in the mask-screen or
Q-spacing produce an unacceptable degree of non-uniformity in the spacing
widths of the black stripes, or guardbands, of the matrix 23. Equation 4
provides a description of the center of the individual exposure profiles
for a given source position. The equation is a very good approximation for
the tension focus mask system, i.e., diffraction has little influence on
the accuracy of the equation. Grouping or degrouping of a triad will be
influenced by the summation of the exposure patterns; however, for a
tension focus mask system with "Q" errors, the center of the individual
exposure profiles described by equation 4 do not track the resultant
grouping of degrouping. For example, the exposure sequence taught by the
entry in column 8 of the TABLE yields grouping with short "Q" that is less
severe than one may expect from equation 4 and, likewise, the degrouping
with long "Q" is less severe than may expect from equation 4. Grouping
refers to the tendency of the red and blue triad centers to move toward
the green center with short Q-error (i.e., b, g and g, r<T/3 in FIG. 3).
Degrouping refers to the tendency of the red and blue triad centers to
move away from the green center with long Q-error (i.e., b, g and g, r>T/3
in FIG. 2).
With reference to FIG. 8, if two of the light source locations are denoted
as B' and R', and are spaced a lateral distance 2 s from the G light
source location, the projected images of the mask openings in each b, g, r
trio at the screen are formed by light rays through three adjacent
openings in the mask, rather than from the same opening, as in FIG. 2. For
the design values L, Q.sub.0, and D.sub.m, the spacings between the images
at the screen are the same as for the procedure of FIG. 2. An example of
this exposure procedure for a conventional CRT is summarized as the entry
in column 4 in the TABLE.
In the presence of Q-spacing errors, the light source configuration of FIG.
8 produces a trio spacing T.sub.2 with the same Q-space dependence as
T.sub.1 in equation (3), but the fractional spacing x.sub.2 /T.sub.2
between the image centers g and b, and between the image centers r and g,
now has the form
x.sub.2 /T.sub.2 =(Q.sub.0 -2.epsilon.)/3Q.sub.0. (5)
With the new source locations, equation (5) states that the fractional
image shifts for a given Q-error are twice as large as in equation (4),
and are in the opposite directions.
For a composite exposure procedure in which the screen is given four
exposure units from each light source in the configuration of FIG. 2, and
an additional two exposure units from each light source location as in
FIG. 8, the projected red and blue slit images experience twice the weight
from the B and R source locations as from the R' and B' source locations.
Additionally, the composite image, contributed by all light sources
associated with a given color, receives the same total exposures of six
units, as in the conventional practice. In the presence of Q-error, the
motions of the red-image and the blue-image centroids from the weighted
type 1 and type 2 exposures cancel each other in the combined exposure.
For sufficiently small Q-errors, on the order of .+-.5% or less, the
contrast level of the composite red or blue image decreases somewhat, but
the peak location and exposure width remain relatively fixed, and exhibit
acceptably small errors.
FIG. 9 illustrates the composite exposure procedure that minimizes the
matrix stripe grouping or de-grouping problems resulting from small
Q-spacing errors. The composite exposure pattern assigns relative exposure
weights of two units from B', four units from R, six units from G, four
units from B, and two units from R'. The procedure is summarized in column
5 of the TABLE.
As previously noted, the lateral shift of the light sources required for
the CRT having the tension focus mask 24 affects only the reference
position of the matrix stripes with respect to the mask slits or openings
33, and has no influence on the matrix opening parity. Matrix opening
parity refers to the condition in which the matrix openings in a given
triad are equal in width. Consequently, shifting the array of the five
light sources in FIG. 9 by a lateral distance of s/2, as summarized for a
left shift in column 6 of the TABLE minimizes the grouping problem, for a
CRT having a tension focus mask, in the presence of Q-errors. In this
example, the mask-screen symmetry axis lies midway between light sources G
and B. Alternatively, the exposure pattern may be shifted right by a
lateral distance s/2 for the same tube type, as summarized in column 7 of
the TABLE.
The weighted 5-position exposure significantly aids in compensating for
stripe-to-stripe spacing errors, and is found adequate for this purpose in
the screen fabrication process for CRT having a tension focus mask.
However, the overall exposure directions in the lighthouse are not
symmetrical about the normal to the screen center, which is also the
symmetry axis for the in-line electron gun assembly of the CRT. A
6-position composite exposure which exhibits such symmetry about the
electron gun and screen axis can be obtained by halving the weights of the
light sources in the exposures of columns 6 and 7 of the TABLE, and
combining the two sequences. The results are shown in FIG. 10 and
summarized in column 8 of the TABLE.
As indicated in step 78 of FIG. 6A, using one of the procedures of either
FIGS. 9 or 10, a xenon light source within the lighthouse exposes the OPC
layer 66 of the photoreceptor 72 to light, which passes through the
plurality of rectangular openings 33 in the tension focus mask 24, to
selectively discharge the more intensely illuminated areas of the OPC
layer 66 of the photoreceptor 72, without completely discharging the less
intensely illuminated areas. Because the intensity of the xenon light
source is substantially less than that of a conventional mercury source,
the underlying photoresist layer 56 of the photoreceptor 72 is
substantially unaffected by this light exposure. Typically, the exposure
voltage contrast between the more intensely illuminated and less intensely
illuminated areas of the OPC layer 66 is about 50-75 volts.
After the exposure step, the tension focus mask 24 is removed from the
panel 12, as indicated by step 80, and the OPC layer 66 is developed, in
step 82, using a suitable liquid toner. The toner comprises negatively
charged pigment particles suspended in an insulating liquid, such as
isopar type H or G. The toner may be applied as a limp stream or by
immersion. During application, the negatively charged toner particles
follow the electrostatic field lines and settle on the protective layer 70
overlying the positively charged, less intensely illuminated, areas of the
OPC layer 66. The excess liquid toner is removed from the panel 12, for
example by gravity flow, or pouring, and the resultant toner lines 84,
shown in FIG. 7, are dried. It has been determined that the exposure dose,
i.e., the number of xenon lamp flashes, directly affects the width of the
toner lines. The width of the lines generally decreases as the exposure
dosage increases. Toner pattern development time, which also affects the
width of the toner lines 84, is related to the conductivity of the toner,
which, in turn, is dependent on the concentration of the pigment solids in
the toner solution. The preferred pigment, available from Olin
Corporation, Cheshire, Conn., comprises carbon particles having a
concentration within the range of 0.3 to 2.0 weight percent. Toner lines
having the necessary density and opacity can be obtained with a liquid
toner having a conductivity of about 0.88 picosiemens/cm (pS/cm), a
charge-to-mass ratio of about 9 microcoulombs/gram (.mu.C/gm), and a
particle size of about 430 nm.
As indicated by step 86, the tension focus mask 24 is re-inserted into the
faceplate panel 12 and mounted within a lighthouse having a mercury arc
source which provides a UV output. Then, as indicated in step 88, of FIG.
6B, the UV radiation source within the lighthouse flood exposes the
photoresist layer 56 of the photoreceptor 72 to UV radiation. The UV
radiation passes through the plurality of rectangular openings 33 in the
tension focus mask 24 and through the protective layer 70, the OPC layer
66, and the OC layer 62, to selectively change the solubility of the
photoresist layer 56 of the photoreceptor 72. The non-illuminated areas of
the photoresist layer 56, underlying the toner lines 84, are unaffected by
the UV exposure and retain their solubility, while the illuminated areas
of the photoresist layer between toner lines are rendered less soluble.
During the UV exposure, the UV source within the lighthouse is oscillated
to prevent the first strands 32 of the tension focus mask 24 from forming
a pattern on the photoresist layer 56.
The toner lines 84 and the various layers 54, 56, 62, 66 and 70, disposed
on the interior surface of the panel 12, are serially developed in order
to expose portions of the interior surface of the viewing faceplate 18. As
indicated in step 90, a suitable quantity of a first solvent is poured
into the panel and sloshed for about two minutes to remove the toner lines
and the protective layer 70. Preferably, the first solvent is selected
from the group consisting of isopropanol (IPA), an aqueous solution of
sulfamic acid (15%), or periodic acid (10%). Then, the panel is tilted
into a vertical position to drain the solvent, toner and protective layer
residue. While in the vertical position, if IPA has been used, an
additional quantity, for example about 200 ml, of IPA is dispensed into
the panel and allowed to drain out, after which the panel sidewall 20 is
wiped dry to remove any residue and the panel is dried. The removal of the
OPC layer 66 is accomplished, as indicated in step 92, by depositing a
second solvent, preferably 400 ml of a 2:1 mixture, by volume, of toluene
and methyl isobutyl ketone (MIBK), or alternatively, a suitable quantity
of d-limonene. The mixture is sloshed around the interior of the panel for
about seven minutes to dissolve the OPC layer 66 and then the panel is
tipped to pour out the solvent mixture and OPC residue. If d-limonene is
used, then no additional treatment is required prior to photoresist
development; however, if the mixture of toluene and MIBK is used, then an
additional 200 ml of toluene is squirted into the panel while it is in a
vertical position for draining, and the sidewall 20 is wiped dry to remove
any residue. Because the OC layer 62 and the unexposed areas of the
photoresist layer 56 are soluble in water, the development of the
photoresist layer, as described in step 94, is accomplished by rinsing the
interior surface of the panel 12 with a third solvent, such as water, to
remove the OC layer and the areas of the photoresist layer having greater
solubility. This development step exposes portions of the underlying areas
of the interior surface of the panel 12, while leaving intact the areas of
the photoresist layer 56 having lesser solubility. The matrix is formed,
as indicated in step 96, by coating the exposed portions of the interior
surface of the panel 12 and the retained areas of the photoresist layer
56, having lesser solubility, with an aqueous graphite suspension, of the
type described in the above-referenced U.S. Pat. No. 3,558,310. The
suspension is dried to form a light-absorbing matrix 23, as indicated in
step 98, and developed, in step 100, by depositing a fourth solvent, such
as aqueous periodic acid, or the equivalent, onto the matrix to soften and
swell the underlying, retained areas of the photoresist layer 56 having
lesser solubility. The matrix is then flushed with water to remove the
loosened, less soluble, retained areas of the photoresist layer and the
overlying matrix thereon, forming openings therein, but leaving the matrix
lines or guardbands attached to the exposed portion of the interior
surface of the panel 12.
The faceplate panel is now ready for the formation of the phosphor screen,
using the EPS process described in U.S. Pat. No. 4,721,767.
While the photoresist layer 56 and the OC layer 62 have been described
herein as separate layers, it is within the scope of this invention to
provide a single layer having both photoresist and conductive properties.
Also, the invention encompasses a suitable development of charged pigment
onto the more intensely illuminated areas of the photoreceptor.
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